Spinach is one of many foods that contains oxalic acid, or oxalate. This naturally occurring chemical is linked to kidney stone formation. Of all foods that contain oxalate, spinach has the highest amount.
USDA Agricultural Research Service scientists have identified eight spinach varieties that are low in oxalate. Researchers analyzed the genetic code of 310 varieties. They found six DNA markers that affect oxalate levels. Research is ongoing.
Other foods that contain oxalate include beets, rhubarb, strawberries, nuts, chocolate, tea, wheat bran, and almost all dry beans. Like spinach, all of these foods can contribute to a healthful diet.